Continuation of investigations of the experimental chemotherapy of schistosomiasis and of the physiological chemistry of schistosomes is in progress. 1. Attempts are being made to define more precisely the structural and conformational requirements for the recently observed antischistosomal activity of nitroheterocyclic compounds and to design on this basis more effective schistosomicidal agents. 2. Attempts are being made to enhance the efficacy of one of these compounds, a nitrovinylfuran, which exhibits high chemotherapeutic activity in animals infected with Schistosoma mansoni and Schistosoma japonicum as well as low toxicity. Studies of the biochemical mode of the antischistosomal action of these compounds are continuing. 3. The relationship between the mutagenicity of hycanthone for mammalian and bacterial cells and the development of resistance to this drug by schistosomes are being explored. 4. The physiological role and the metabolism of 5-hydroxytryptamine and of norepinephrine in schistosomes and in an intermediate molluscan schistosome host, Biomphalaria glabrata, are being investigated.